The shelf life of LIFEPO4 batteries is supposed to be in the 2,000 cycle range, (which is a very long time) for quality manufacturers. China is the maker of most of these, because the labour involved and toxicity. Some use quality ingredients from "Phostec" in Canada who hold a patent on some of these powders.
www.ebike.ca is a supplier of 24, 36, and 48 volt 12 AH batteries, and test them etc.
LIFEPO4 is still in the infancy stages but for safety and dollar for watt/ hour of use, it is the chemistry of choice, I bought a 48 volt 12ah for my bike and will keep you guys posted of the results as i also have a Cycle Analyst to record everything that's going on.
Most people that report problems are the BMS (battery managament System) attached to these batteries to keep them balanced and from over discharge which can damage them permanently. But a good supplyer will replace these at no cost, and they are getting better by the day.